This invention relates to a projection-type display device for magnifying an image formed on a liquid crystal light valve and projecting it on a screen.
The conventional projection-type display device shown in FIG. 1 is comprised mainly of: a light source 1 that emits a parallel luminous flux L.sub.1 in one direction; a liquid crystal light valve 2 that changes the distribution of a luminous flux L.sub.2 which passes through and changes the contrast of a rectangular image; and a projection lens 3 which magnifies luminous flux L.sub.2 and projects on screen S a rectangular image (for example, under the NTSC standard a rectangle in which the proportion of the long side to the short is 4:3). Here, light source 1 comprises a parabolic mirror 4 and a lamp 5 (for example a metal halide lamp or xenon lamp), the center of luminescence of which is at the focal point of parabolic mirror 4. The reference numeral 6 designates a condenser lens.
However, because the luminous flux L.sub.1 emitted by the projection-type display device described above is of circular cross section, that portion of the luminous flux impinging on the periphery of the rectangular display area of liquid crystal light valve 2 made no contribution to projecting the image. FIG. 2 is for the purpose of clarifying this point, and shows that the hatched portion within the circular cross section of luminous flux L.sub.1 is the portion that makes no contribution to projecting the image.
It can thus be seen that with conventional projection-type display devices, a portion of the luminous flux emitted from light source 1 is wasted, and this fact inhibits efforts to increase the brightness of the projected image.
Also, the direct divergent beam from the lamp 5 ((d) of FIG. 2) is not used to make the image on the screen, because obscured by the liquid crystal light valve 2.